A. Field of the Invention
This invention relates to a method for manufacturing a perpendicular magnetic recording medium mounted in various magnetic recording devices.
B. Description of the Related Art
Perpendicular magnetic recording methods are being adopted as technology to realize high densities in magnetic recording. A perpendicular magnetic recording medium has a configuration which includes at least a magnetic recording layer formed from hard magnetic material, and which further optionally includes a under layer formed from a soft magnetic material which serves to concentrate magnetic flux generated by the magnetic head in the magnetic recording layer, an under layer to orient the magnetic recording layer in an intended direction, a protective film which protects the surface of the magnetic recording layer, and similar.
As materials used to form the magnetic recording layer of a perpendicular magnetic recording medium, CoCrPt, CoCrTa, and other alloy materials with SiO2, TiO2 or other nonmagnetic materials added to form a granular magnetic film have been proposed (see Japanese Patent Application Laid-open No. 2001-291230, Japanese Patent Application Laid-open No. H08-083418, and WO 02/039433). For example, in a CoCrPt—SiO2 granular magnetic film, nonmagnetic SiO2 is segregated so as to surround the periphery of CoCrPt magnetic crystal grains, and by means of this nonmagnetic SiO2, individual CoCrPt magnetic crystal grains are magnetically separated.
In recent years there has been a pressing need to reduce the grain diameters of magnetic crystal grains in granular magnetic films and further raise the recording densities of perpendicular magnetic recording media. On the other hand, reduction of the grain sizes of magnetic crystal grains lowers the thermal stability of recorded magnetization. Consequently in order to compensate for the lowered thermal stability due to reduced grain sizes of magnetic crystal grains, formation of the magnetic crystal grains in granular magnetic films using materials with higher magnetocrystalline anisotropy has been sought.
Among materials having the desired high magnetocrystalline anisotropy, there are L10 ordered alloys, and various methods have been proposed for manufacturing thin films of L10 ordered alloys (see Patent Publication No. 3318204, Patent Publication No. 3010156, Japanese Patent Application Laid-open No. 2001-101645, Japanese Patent Application Laid-open No. 2004-178753, and Japanese Translation of PCT Application No. 2010-503139). On the other hand, in magnetic recording media, nonmagnetic bases of aluminum or glass have been used in consideration of strength, shock resistance and other properties. When depositing an L10 ordered alloy onto such a nonmagnetic base, the under layer is important. This is because in order to impart high magnetocrystalline anisotropy, the crystals of the L10 ordered alloy must have an (001) orientation (the crystal [001] axis must be perpendicular to the plane of the base). To this end, generally MgO, which has an appropriate lattice mismatch (good lattice matching) with L10 ordered alloys, is used as the under layer.
Further, with the goal of improving the adhesion property with a magnetic recording layer comprising an L10 ordered alloy and an under layer, it has been proposed that in place of MgO, an under layer can be used comprising {100} orientation NaCl-type crystal, {100} orientation CsCl-type crystal, intermetallic compound having a {001} orientation L10 type structure, or intermetallic compound having a {001} orientation L12 type structure, and having a lattice constant of from 3.52 Å to 4.20 Å (see Japanese Patent Application Laid-open No. 2001-189010). In this document, the MgO under layer is formed using an RF sputtering method. There is no description of the target to be used.
One problem when forming an MgO film is low productivity. That is, because MgO has low electrical conductivity, when forming an MgO film by a sputtering method using an MgO target, it has been necessary to use an RF sputtering method. However, the rate of film deposition of RF sputtering methods is lower than the film deposition rate for DC sputtering methods normally used in the manufacture of magnetic recording media. Due to the low film deposition rate, RF sputtering methods are not well-suited to mass production of magnetic recording media, for which productivity of from 400 to 1000 units per hour are required for each film production line. In addition to improving productivity of magnetic recording media, from the standpoints of cost reduction and stability of manufacturing equipment, it is desirable that a DC sputtering method be used for MgO film.
Further, when an MgO under layer is formed by a sputtering method in an atmosphere not containing oxygen, oxygen deficiency occurs in the crystal structure of the MgO film formed, and the MgO crystallinity is harmed. Hence an MgO film formation method which can suppress oxygen deficiency and maintain crystallinity is desired.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.